Set up IaC for Elastic Cloud Hosted Cluster Management

DRI

@poneill

This issue will address the second stage of moving Elastic Cloud configuration to IAC via Terraform as discussed originally here

Set up cluster management using the terraform provider -- https://registry.terraform.io/providers/elastic/elasticstack/latest/docs/guides/elasticstack-and-cloud.

This will replace all the jsonnet in https://gitlab.com/gitlab-com/runbooks/-/tree/master/elastic?ref_type=heads, plus manage rules, users and things like oauth settings, all of which are not managed by IaC today. This will be required to be performed for the 3 currently managed cloud elasticsearch deployments - monitoring, gitlab-logs-nonprod and gitlab-logs-prod.

Risks ⚠️ : To avoid breaking clusters this will likely require much iteration to add the cluster configuration piece by piece to IAC.

Status 2025-10-15

🚧 The work specified in this issue is currently in progress.

MR's are now ready to review for part of this work. Following MR's are imports only and should be safe to run against current deployed infrastructure without creation or destruction of resources. Once the MR for the relevant resource has been applied then the related config can be removed from the runbooks repo.

Full Status Update with MRs: #4342 (comment 2822868844)